Low temperature sintered ceramic capacitor with a temperature compensating capability, and method of manufacture

ABSTRACT

A temperature compensating capacitor of monolithic or multilayered configuration comprising a dielectric ceramic body and at least two electrodes buried therein. The ceramic body is composed of a major ingredient expressed by the formula, {(Sr 1-x  Ca x )O} k  (Ti 1-y  Zr y )O 2 , where x, k and y are numerals in the ranges of 0.005 to 0.995 inclusive, 1.00 to 1.04 inclusive, and 0.005 to 0.100 inclusive, respectively. To this major ingredient is added a minor proportion of a mixture of lithium oxide, silicon dioxide, and one or more metal oxides selected from among barium oxide, magnesium oxide, zinc oxide, strontium oxide and calcium oxide. For the fabrication of capacitors the mixture of the above major ingredient and additives in finely divided form are formed into moldings of desired shape and size, each with at least two electrodes buried therein. The moldings and electrodes are cosintered in a reductive or neutral atmosphere and then are reheated at a lower temperature in an oxidative atmosphere. the cosintering temperature can be so low that nickel or like base metal can be employed as the electrode material.

BACKGROUND OF THE INVENTION

Our invention relates to solid dielectric capacitors, and morespecifically to ceramic capacitors such as those of the monolithic,multilayered configuration that are capable of manufacture bycosintering at sufficiently low temperatures to permit the use of basemetal electrodes, and to process for the fabrication of such lowtemperature sintered capacitors. The ceramic capacitors of our inventionare particularly notable for their temperature compensating capability,having a practically constant temperature coefficient of capacitance inthe normal range of temperatures in which they are intended for use.

We know several conventional ceramic compositions calculated to permitthe use of base metal electrodes in the manufacture of monolithic,multilayered ceramic capacitors by cosintering of the base metalelectrodes and the dielectric ceramic bodies. Among such known ceramiccompositions, and perhaps most pertinent to our present invention, arethose described and claimed in Japanese Laid Open Patent Application No.59-227769, which compositions comprise a major proportion of a primaryingredient expressed by the formula, {(Sr_(1-x) Ca_(x))O}_(k) TiO₂, andminor proportions of lithium oxide (Li₂ O), silicon dioxide (SiO₂), andone or more of barium oxide (BaO), calcium oxide (CaO), and strontiumoxide (SrO). In the manufacture of ceramic capacitors the dielectricbodies of these known compositions are sinterable in a reductiveatmosphere, so that electrodes of nickel or like base metal can beemployed and buried in the dielectric bodies for cosintering to maturitywithout the danger of oxidation. The resulting capacitors have aremarkable temperature compensating capability.

However, the temperature compensating capacitors of the above knownceramic composition are unsatisfactory in that their Q factors are lessthan 4400 when their temperature coefficients of capacitance are in therange of -1000 to +350 parts per million (ppm) per degree centigrade(C.). We have been keenly aware of great demands on temperaturecompensating ceramic capacitors of higher performance characteristicsand smaller size.

SUMMARY OF THE INVENTION

We have hereby discovered how to improve the performancecharacteristics, particularly Q factor and resistivity, of thetemperature compensating ceramic capacitors of the class underconsideration.

Stated briefly in one aspect thereof, our invention provides a lowtemperature sintered solid dielectric capacitor comprising a dielectricceramic body and at least two electrodes in contact therewith. Thedielectric ceramic body consists essentially of: (a) 100 parts by weightof {(Sr_(1-x) Ca_(x))O}_(k) (Ti_(1-y) Zr_(y))O₂, where x is a numeral inthe range of 0.005 to 0.995 inclusive, k a numeral in the range of 1.00to 1.04 inclusive, and y a numeral in the range of 0.005 to 0.100inclusive; and (b) 0.2 to 10.0 parts by weight of an additive mixture ofLi₂ O, SiO₂, and at least one metal oxide selected from the groupconsisting of BaO, magnesium oxide (MgO), zinc oxide (ZnO), SrO and CaO.The relative proportions of Li₂ O, SiO₂ and at least one selected metaloxide, altogether constituting the additive mixture, will bespecifically determined in connection with a ternary diagram attachedhereto.

The ceramic capacitor of our invention, having its dielectric bodyformulated as set forth in the foregoing, has proved to be very wellsuited for temperature compensating applications in oscillator and othercircuits. The test capacitors manufactured in accordance with ourinvention had Q factors of 4500 or more and resistivities of 1.0×10⁷megohm-centimeters or more while at the same time their temperaturecoefficients of capacitances were both in and outside the range of -1000to +350 ppm per degree C. It is therefore possible to reduce the size ofthe prior art ceramic capacitors of the noted compositions withoutsacrifice in their performance characteristics.

Another aspect of our invention concerns a method of fabricating theabove defined ceramic capacitor. The method dictates, first of all, thepreparation of a mixture of the above indicated proportions of the majoringredient and additives in finely divided form. This mixture is thenmolded into a body of desired shape and size, which is provided with atleast two electrode portions of an electroconductive material in anyconvenient manner. Then the molding with the electrode portions issintered in a nonoxidative (i.e. reductive or neutral) atmosphere and issubsequently reheated in an oxidative atmosphere.

We recommend a temperature range of 1000° to 1200° C. for sintering thedielectric molding. This temperature range is sufficiently low to permitthe cosintering, in a reductive or neutral atmosphere of nickel or likebase metal electrodes on the dielectric molding without the likelihoodof the flocculation or diffusion of the base metal.

The above and other features and advantages of our invention and themanner of realizing them will become more apparent, and the inventionitself will best be understood, from a study of the followingdescription and appended claims taken together with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional representation of a monolithic, multilayeredceramic capacitor in accordance with our invention, the illustratedcapacitor being representative of numerous test capacitors fabricated inthe Examples of our invention to be presented subsequently; and

FIG. 2 is a ternary diagram depicting the relative proportions of theadditives of the ceramic compositions in accordance with our invention.

DETAILED DESCRIPTION

We have illustrated in FIG. 1 one of many monolithic ceramic capacitorsof identical construction fabricated in the subsequent Examples of ourinvention by way of a preferable embodiment thereof. Generallydesignated 10, the representative capacitor is shown to have aninterlamination of three dielectric ceramic layers 12 and two filmelectrodes 14. The three ceramic layers 12 constitute in combination asolid dielectric body 15 having the low temperature sintered ceramiccompositions in accordance with our invention. The two film electrodes14, which can be of a low cost base metal such as, typically, nickel,extend from the opposite sides of the dielectric body 15 toward, andterminate short of, the other sides of the dielectric body and so havean overlapping, parallel spaced relation to each other. A pair ofconductive terminations 16 contact the respective film electrodes 14.Each termination 16 is shown to comprise a baked on zinc layer 18, aplated on copper layer 20, and a plated on solder layer 22.

Typically, and as fabricated in the subsequent Examples of outinvention, the intermediate one of the three dielectric layers 12 has athickness of 0.02 millimeter. The area of that part of each filmelectrode 14 which overlaps the other film electrode is 25 squaremillimeters (5×5 millimeters).

Examples

We fabricated 63 different sets of test capacitors each constructed asin FIG. 1, some having their dielectric bodies formulated in accordancewith the ceramic compositions of our invention and others not, andmeasured their electrical properties. Table 1 lists the compositions ofthe dielectric bodies of all the test capacitors fabricated.

We have defined the major ingredient of the ceramic compositions inaccordance with our invention as (Sr_(1-x) Ca_(x))O_(k) (Ti_(1-y)Zr_(y))O₂. Accordingly, in Table 1, we have given various combinationsof the atomic numbers k, x and y in the formula to indicate the specificmajor ingredients employed in the various Tests. The ceramiccompositions of our invention further include mixtures, in variousproportions, of additives Li₂ O, SiO₂ and a metal oxide or oxides (MO).Table 1 specifies the amounts, in parts by weight, of the additivemixtures with respect to 100 parts by weight of the major ingredient, aswell as the relative proportions, in mole percent, of the additives Li₂O, SiO₂ and MO. Further, since MO can be any one or more of BaO, MgO,ZnO, SrO and CaO, Table 1 gives the relative proportions, in molepercent, of these metal oxides, wherever one or more of them areemployed.

                                      TABLE 1                                     __________________________________________________________________________    Ceramic Compositions                                                          Major Ingredient                                                                             Additives                                                      Test                                                                             (100 wt. parts)                                                                           Amount                                                                             Composition (mole %)                                                                     MO (mole %)                                    No.                                                                              k   x   y   (wt. part)                                                                         Li.sub.2 O                                                                        SiO.sub.2                                                                        MO  BaO                                                                              MgO                                                                              ZnO                                                                              SrO                                                                              CaO                                __________________________________________________________________________     1 1.01                                                                              0.39                                                                              0.05                                                                              2.0   0  65 35  20 20 20 20 20                                  2 "   "   "   "    "   60 40  "  "  "  "  "                                   3 "   "   "   "     5  45 50  "  "  "  "  "                                   4 "   "   "   "    50  50  0  -- -- -- -- --                                  5 "   "   "   "    25  75 --  -- -- -- -- --                                  6 "   "   "   "    15  "  10  20 20 20 20 20                                  7 "   "   "   "     5  70 25  "  "  "  "  "                                   8 "   "   "   "    15  45 40  "  "  "  "  "                                   9 "   "   "   "    30  "  25  "  "" "  "                                     10 "   "   "   "    45  40 15  "  "  "  "  "                                  11 "   "   "   "    15  65 20  100                                                                              -- -- -- --                                 12 "   "   "   "    "   "  "   -- 100                                                                              -- -- --                                 13 "   "   "   "    "   "  "   -- -- 100                                                                              -- --                                 14 "   "   "   "    "   "  "   -- -- -- 100                                                                              --                                 15 "   "   "   "    "   "  "   -- -- -- -- 100                                16 "   "   "   "    "   "  "   20 20 20 20 20                                 17 1.02                                                                              "   "   "    15  70 15  "  "  "  "  "                                  18 "   "   "   "     5  65 30  -- 10 10 40 40                                 19 "   "   "   "    15  50 35  10 -- 30 20 "                                  20 "   "   "   "    35  "  15  30 10 -- "  "                                  21 "   "   "   "    "   65  0  10 "  10 -- 70                                 22 "   "   "   "    25  65 10  30 20 20 30 --                                 23 "   "   "   "    20  60 20  20 10 40 10 20                                 24 "   "   "   "    40  55  5  "  40 10 20 10                                 25 1.01                                                                               0.005                                                                            "   "    10  60 30  20 20 20 20 20                                 26 "   0.20                                                                              "   "    "   "  "   "  "  "  "  "                                  27 "   0.30                                                                              "   "    "   "  "   "  "  "  "  "                                  28 "   0.39                                                                              "   "    "   "  "   "  "  "  "  "                                  29 "   0.55                                                                              "   "    "   "  "   "  "  "  "  "                                  30 "    0.995                                                                            "   "    "   "  "   "  "  "  "  "                                  31 1.03                                                                              0.38                                                                               0.002                                                                            "    20  65 15  "  "  "  "  "                                  32 "   "    0.005                                                                            "    "   "  "   "  "  "  "  "                                  33 "   "   0.03                                                                              "    "   "  "   "  "  "  "  "                                  34 "   "   0.05                                                                              "    "   "  "   "  "  "  "  "                                  35 "   "   0.10                                                                              "    "   "  "   "  "  "  "  "                                  36 "   "   0.12                                                                              "    "   "  "   "  "  "  "  "                                  37 "   0.65                                                                               0.002                                                                            "    15  55 30  "  "  "  "  "                                  38 "   "    0.005                                                                            "    "   "  "   "  "  "  "  "                                  39 "   "   0.02                                                                              "    "   "  "   "  "  "  "  "                                  40 "   "   0.03                                                                              "    "   "  "   "  "  "  "  "                                  41 "   "   0.05                                                                              "    "   "  "   "  "  "  "  "                                  42 "   "   0.10                                                                              "    "   "  "   "  "  "  "  "                                  43 "   "   0.12                                                                              "    "   "  "   "  "  "  "  "                                  44 1.0 0.34                                                                              0.02                                                                              0    10  65 25  "  "  "  "  "                                  45 "   "   "   0.2  "   "  "   "  "  "  "  "                                  46 "   "   "   1    "   "  "   "  "  "  "  "                                  47 "   "   "   3    "   "  "   "  "  "  "  "                                  48 "   "   "   5    "   "  "   "  "  "  "  "                                  49 "   "   "   10   "   "  "   "  "  "  "  "                                  50 "   "   "   12   "   "  "   "  "  "  "  "                                  51 0.99                                                                              0.40                                                                              0.03                                                                              2.0  25  70  5  "  "  "  "  "                                  52 1.00                                                                              "   "   "    "   "  "   "  "  "  "  "                                  53  1.005                                                                            "   "   "    "   "  "   "  "  "  "  "                                  54 1.01                                                                              "   "   "    "   "  "   "  "  "  "  "                                  55 1.02                                                                              "   "   "    "   "  "   "  "  "  "  "                                  56 1.03                                                                              "   "   "    "   "  "   "  "  "  "  "                                  57 1.04                                                                              "   "   "    "   "  "   "  "  "  "  "                                  58 0.99                                                                              0.60                                                                              "   3.0  25  50 25  "  "  "  "  "                                  59 1.00                                                                              "   "   "    "   "  -   -  "  "  "  "                                  60 1.01                                                                              "   "   "    "   "  "   "  "  "  "  "                                  61 1.02                                                                              "   "   "    "   "  "   "  "  "  "  "                                  62 1.04                                                                              "   "   "    "   "  "   "  "  "  "  "                                  63 1.05                                                                              "   "   "    "   "  "   "  "  "  "  "                                  __________________________________________________________________________

According to Table 1, the major ingredient of the dielectric bodies ofthe capacitors of Test No. 1 was {(Sr₀.61 Ca₀.39)O}₁.01 (Ti₀.95Zr₀.05)O₂. One hundred parts of this major ingredient was admixed with2.0 parts by weight of a mixture of 65 mole percent SiO₂ and 35 molepercent MO. MO was a mixture of 20 mole percent BaO, 20 mole percentMgO, 20 mole percent ZnO, 20 mole percent SrO and 20 mole percent CaO.Li₂ O was not used in this particular Test.

For the fabrication of the capacitors of Test No. 1 we started with thepreparation of the major ingredient of their dielectric bodies. Weprepared the following start materials;

Strontium carbonate (SrCO₃)

513.82 grams (0.61 mole part)

Calcium carbonate (CaCO₃)

222.54 grams (0.39 mole part)

Titanium oxide (TiO₂)

428.83 grams (0.95 mole part)

Zirconium oxide (ZrO₂)

34.81 grams (0.05 mole part)

These start materials had all purities of not less than 99.0 percent.The above specified weights of the start materials do not include thoseof the impurities contained. We charged the start materials into a potmill together with alumina balls and 2.5 liters of water and mixed themtogether for 15 hours. Then the mixture was introduced into a stainlesssteel vat and therein dried by air heated to 150° C. for four hours.Then the dried mixture was crushed into relatively coarse particles,which were subsequently fired in air within a tunnel furnace at 1200° C.for two hours. There was thus obtained the major ingredient of the abovespecified composition in finely divided form.

For the provision of the additives of Test No. 1 we prepared:

    ______________________________________                                        SiO.sub.2   49.61  grams (65 mole percent)                                    BaCO.sub.3  17.55  grams (seven mole percent)                                 MgO         3.58   grams (seven mole percent)                                 ZnO         7.24   grams (seven mole percent)                                 SrCO.sub.3  13.13  grams (seven mole percent)                                 CaCO.sub.3  8.89   grams (seven mole percent)                                 ______________________________________                                    

To these substances we added 300 cubic centimeters of alcohol, and theresulting slurry was stirred for 10 hours in a polyethylene pot withalumina balls. Then the mixture was air fired at 1000° C. for two hours.Then, charged into an alumina pot together with 300 cubic centimeters ofwater, the fired mixture was pulverized with alumina balls over a periodof 15 hours. Then the pulverized mixture was dried at 150° C. for fourhours. There was thus obtained in finely divided form the desiredadditive mixture of 65 mole percent SiO₂ and 35 mole percent MO, withthe MO consisting of seven mole percent BaO, seven mole percent MgO,seven mole percent ZnO, seven mole percent SrO, and seven mole percentCaO.

Twenty grams (two weight percent) of this additive mixture was added to1000 grams of the above prepared major ingredient. Further, to thismixture, we added 15 percent by weight of an organic binder and 50percent by weight of water with respect to the total weight of the majoringredient and additives. The organic binder was an aqueous solution ofacrylic ester polymer, gylcerine, and condensed phosphate. The mixtureof all these was ball milled into a slurry. Then this slurry wasdefoamed in vacuum.

Then the defoamed slurry was charged into a reverse roll coater therebyto be shaped into a thin, continuous strip on an elongate supportingstrip of polyester film. Then the strip was dried by heating to 100° C.on the supporting film. The green ceramic strip thus obtained,approximately 25 microns thick, was subsequently punched into "squares"sized 10 by 10 centimeters. These green ceramic squares are to becomethe ceramic layers 12, FIG. 1, in the completed test capacitors 10.

For the fabrication of the base metal film electrodes 14 on the ceramiclayers 12, we prepared 10 grams of nickel in finely divided form, withan average particle size of 1.5 microns, and a solution of 0.9 gram ofethyl celllose in 9.1 grams of butyl "Carbitol" (trademark fordiethylene glycol monobutyl ether). Both were intimately interminged bybeing agitated for 10 hours, thereby providing an electroconductivepast. Then this paste was "printed" on one surface of each green ceramicsquare, which had been prepared as above described, through a screenhaving 50 perforations of rectangular shape, each sized seven by 14millimeters.

After drying the printed past, two green squares were stacked, withtheir printings directed upwardly, and with the printings on the twosquares offset from each other to an extent approximately half the pitchof their patterns in the longitudinal direction. The thus stacked twoprinted squares were placed between two separate stacks of fourunprinted squares each with a thickness of 60 microns. The resultingstack of printed and unprinted squares were pressed in their thicknessdirection under a pressure of approximately 40 tons at 50° C., therebyfirmly bonding the stacked squares to one another. Then the bondedsquares were cut in a latticed pattern into 50 laminate chips ofidentical construction.

We employed a furnace capable of atmosphere control for cofiring theabove prepared green dielectric bodies and, buried therein, theconductive layers which were to become the film electrodes 14 in thecompleted capacitors 10. The chips were first air heated in this furnaceto 600° C. at a rate of 100° C. per hour, thereby driving off theorganic binder that had been used for providing the slurry of thepowdered major ingredient and additives. Then the furnace atmosphere waschanged from air to a reductive (nonoxidative) atmosphere consisting oftwo percent by volume of molecular hydrogen and 98 percent by volume ofmolecular nitrogen. In this reductive atmosphere the furnace temperaturewas raised from 600° C. to 1160° C. at a rate of 100° C. per hour. Themaximum temperature of 1160° C., at which the ceramic bodies formulatedin accordance with our invention were to be sintered to maturity, wasmaintained for three hours. Then the furnace temperature was lowered to600° C. at a rate of 100° C. per hour. Then, with the furnace atmosphereagain changed to air (oxidative atmosphere), the temperature of 600° C.was maintained for 30 minutes for the oxidizing heat treatment of thesintered chips. Then the furnace temperature was allowed to drop to roomtemperature.

There were thus obtained the dielectric ceramic bodies 15, FIG. 1,cosintered with the film electrodes 14 buried therein.

We proceeded to the production of the pair of conductive terminations 16on both sides of each ceramic body 15 through which are exposed the filmelectrodes 14. First, for the production of the inmost zinc layers 18, aconductive paste composed of zinc, glass frit and vehicle was coated onboth sides of each ceramic body 15. The coatings on drying were airheated to 550° C. and maintained at that temperature for 15 minutes,thereby completing the zinc layers 18 each in direct contact with one ofthe two film electrodes 14. Then the intermediate copper layers 20 wereformed over the zinc layers 18 by electroless plating. Then theoutermost solder layers 22 were formed by electroplating a lead tinalloy over the copper layers 20.

We have thus completed the fabrication of monolithic, multilayeredceramic test capacitors, each constructed as in FIG. 1, in accordancewith the ceramic composition of Test No. 1 of Table 1. The compositionof the ceramic bodies 15 of the thus completed capacitors provedsubstantially akin to that before sintering. It is therefore reasonedthat the sintered ceramic bodies 15 are of perovskite structures, withthe additives (65 mole percent SiO₂, seven mole percent BaO, seven molepercent MgO, seven mole percent ZnO, seven mole percent SrO, and sevenmole percent CaO) uniformly dispersed among the crystal grains of themajor ingredient.

As for the other ceramic compositions of Table 1, designated Tests Nos.2 through 63, we made similar capacitors through exactly the sameprocedure as that set forth in the foregoing in connection the Test No.1 composition, except for the temperature of sintering in the reductiveatmosphere, which will be referred to presently.

All the capacitors of Test Nos. 1 through 63 were then tested as totheir specific dielectric constants, temperature coefficients, Qfactors, and resistivities. The following are the methods we employedfor the measurement of these properties:

Specific Dielectric Constant

The capacitance of each test capacitor was first measured at atemperature of 20° C., a frequency of one megaherts, and an effectivealternating current voltage of 0.5 volt. Then the specific dielectricconstant was computed from the measured value of capacitance, the area(25 square millimeters) of each of the overlapping parts of the two filmelectrodes 14, and the thickness (0.05 millimeter) of that ceramic layer12 which intervenes between the film electrodes.

Temperature Coefficient of Capacitance

The capacitance C₈₅ at 85° C. and capacitance C₂₀ at 20° C. of each testcapacitor were first measured. Then the temperature coefficient TC ofcapacitance was computed by the equation ##EQU1##

Q Factor

The Q factor was measured by a Q meter at a frequency of one megahertz,a temperature of 20° C., and an effective alternating current voltage of0.5 volt.

Resistivity

Resistance between the pair of conductive terminations 16 of each testcapacitor was measured after the application of a direct current voltageof 50 volts for one minute at a temperature of 20° C. Then theresistivity was computed from the measured resistance value and the sizeof the test capacitors.

Table 2 gives the results of the measurements by the above describedmethods, as well as the maximum temperatures at which the testcapacitors were sintered in the reductive atmosphere during theirmanufacture. It will be noted from this table that the specificdielectric constants of the Test No. 1 capacitors, for instance,averaged 265, their temperature coefficients -880 ppm per degree C.,their Q factors 9600, and their resistivities 1.1×10⁷megohm-centimeters. The temperature coefficients of the capacitances ofthe test capacitors were practically constant in the normal range oftheir operating temperatures, making the capacitors well suited for useas temperature compensating capacitors.

                  TABLE 2                                                         ______________________________________                                        Firing Temperature & Capacitor Characteristics                                       Electrical Properties                                                                         Temperature                                                 Firing  Specific  Coefficient of                                         Test Temp.   Dielectric                                                                              Capacitance                                                                            Q     Resistivity                             No.  (°C.)                                                                          Constant  (ppm/°C.)                                                                       Factor                                                                              (megohm-cm)                             ______________________________________                                         1   1160    265       -880     9600  1.1 × 10.sup.7                     2   1160    "         -870     9500  1.2 × 10.sup.7                     3   1150    270       "        9700  1.3 × 10.sup.7                     4   1130    272       -880     9800  1.8 × 10.sup.7                     5   "       270       "        "     1.5 × 10.sup.7                     6   1290    Not coherently bonded of firing.                                  7   "       "                                                                 8   "       "                                                                 9   "       "                                                                10   "       "                                                                11   1140    276       -900     9700  1.8 × 10.sup.7                    12   "       280       -880     9600  2.0 × 10.sup.7                    13   "       269       -850     9200  1.4 × 10.sup.7                    14   "       273       -890     9800  1.8 ×  10.sup.7                   15   "       270       -870     "     1.7 × 10.sup.7                    16   "       272       "        9700  1.6 × 10.sup.7                    17   1130    270       "        9800  2.0 × 10.sup.7                    18   1140    267       -865     9700  1.8 × 10.sup.7                    19   "       271       -880     9800  1.6 × 10.sup.7                    20   "       272       -900     10000 "                                       21   "       270       -890     9800  1.8 × 10.sup.7                    22   "       275       -900     "     1.7 × 10.sup.7                    23   "       269       -850     9500  1.3 × 10.sup.7                    24   "       276       -890     9800  2.2 × 10.sup.7                    25   1110    338       -3350    12000 3.7 × 10.sup.7                    26   "       315       -2500    10000 "                                       27   1120    290       -1800    "     1.9 × 10.sup.7                    28   1130    270       -850     "     1.4 × 10.sup.7                    29   1120    265       -1300    9500  2.1 × 10.sup.7                    30   1100    168       -1950    8000  2.2 × 10.sup.7                    31   1140    215       -800     4500  8.5 × 10.sup.6                    32   1130    230       "        6100  1.0 × 10.sup.7                    33   "       240       "        8500  1.1 × 10.sup.7                    34   1140    255       -850     9800  1.7 × 10.sup.7                    35   1160    240       -1300    9000  5.2 × 10.sup.7                    36   1250    Not coherently bonded on firing.                                 37   1130    140       -1100    4600  9.2 × 10.sup.6                    38   "       150       -1120    6300  1.0 × 10.sup.7                    39   1120    155       "        6500  1.2 × 10.sup.7                    40   "       160       -1150    7000  1.3 × 10.sup.7                    41   1140    190       -1200    8400  1.9 × 10.sup.7                    42   1160    180       -1800    7300  5.3 × 10.sup.7                    43   1250    Not coherently bonded on firing.                                 44   "       "                                                                45   1170    242       -1000    8000  1.5 × 10.sup.7                    46   1150    240       "        7600  1.4 × 10.sup.7                    47   1130    238       "        7000  1.3 × 10.sup.7                    48   1110    235       -995     6300  1.2 × 10.sup.7                    49   1050    220       -992     4500  1.0 × 10.sup.7                    50   1030    217       -987     1300  9.5 × 10.sup.6                    51   1140    270       -600     1100  3.0 × 10.sup.3                    52   "       255       -1000    8000  1.0 × 10.sup.7                    53   "       256       -980     9000  "                                       54   "       257       -1010    8800  "                                       55   1150    260       -1020    8700  1.1 × 10.sup.7                    56   1160    "         -1030    8000  1.3 × 10.sup.7                    57   1180    261       -1050    7000  1.8 × 10.sup.7                    58   1130    232       -570      600  2.8 × 10.sup.3                    59   "       210       -1500    7200  1.7 × 10.sup.3                    60   "       "         -1480    "     1.7 × 10.sup.7                    61   1140    215       -1490    7000  2.0 × 10.sup.7                    62   1170    220       -1500    6000  3.0 × 10.sup.7                    63   1260    Not coherently bonded on firing.                                 ______________________________________                                    

It will be observed from Table 2 that the dielectric bodies of TestsNos. 6-10, 36, 43, 44 and 63 were not coherently bonded on firing attemperatures as high as 1250° to 1290° C. in the reductive atmosphere.The corresponding ceramic compositions of Table 1 fall outside the scopeof our invention. The dielectric bodies of all the other Tests could besintered to maturity at temperatures less than 1200° C.

Before proceeding further with the examination of the results of Table 2we will determine the acceptable criteria of the four electricalproperties in question for the temperature compensating ceramiccapacitors provided by our invention. These criteria are:

Specific dielectric constant:

From 140 to 338.

Temperature coefficient of capacitance:

From -3400 to -800 ppm per degree C.

Q factor:

Not less than 4500.

Resistivity:

Not less than 1.0×10⁷ megohm-centimeters.

A reconsideration of Table 1 in light of the above established criteriaof favorable electrical characteristics will reveal that the capacitorsof Tests Nos. 31, 37, 50, 51 and 58 do not meet these criteria.Accordingly, the corresponding ceramic compositions of Table 1 also falloutside the scope of our invention. All the test capacitors but those ofTests Nos. 6-10, 31, 36, 37, 43, 44, 50, 51, 58 and 63 satisfy thecriteria, so that their ceramic compositions are in accord with ourinvention.

Now, let us study the ceramic compositions of Table 1 and thecorresponding capacitor characteristics, as well as the sinteringtemperatures, of Table 2 in more detail. The ceramic compositions ofTest No. 44 contained no additive specified by our invention. Thedielectric bodies formulated accordingly were not coherently bonded onfiring at a temperature as high as 1250° C. Consider the ceramiccompositions of Test No. 45 for comparison. They contained 0.2 part byweight of the additives with respect to 100 parts by weight of the majoringredient. Even though the firing temperature was as low as 1170° C.,the resulting test capacitors possess the desired electricalcharacteristics. We set, therefore, the lower limit of the possibleproportions of the additive mixture at 0.2 part by weight with respectto 100 parts by weight of the major ingredient.

The Test No. 50 ceramic composition contained as much as 12 parts byweight of the additives with respect to 100 parts by weight of the majoringredient. The resulting capacitors have an average Q factor of 1300and an average resistivity of 9.5×10⁶, which are both less than theabove established criteria. When the proportion of the additive mixturewas reduced to 10 parts by weight, as in Test No. 49, the resultingcapacitors have all the desired characteristics. Therefore, the upperlimit of the possible proportions of the additive mixture is set at 10parts by weight with respect to 100 parts by weight of the majoringredient.

As for the major ingredient, the value of x was variously determinedfrom 0.005 to 0.995 in Tests Nos. 25-29. The characteristics of theresulting capacitors all came up to the above criteria. The value of xcan thus be anywhere between these limits.

The value of y was set at 0.002 in Tests Nos. 31 and 37. Thecharacteristics of the resulting capacitors were unsatisfactory,reflecting no effect of the use of ZrO₂ in the major ingredient. Whenthe value of y was increased to 0.005 as in Tests Nos. 32 and 38, theresulting capacitors had all the desired characteristics. We set,therefore, the lowermost value of y at 0.005. The value of y was made ashigh as 0.12 in Tests Nos. 36 and 43. The resulting dielectric bodieswere not coherently bonded on firing at 1250° C. The capacitors of thedesired characteristics could be obtained when the value of y wasdecreased to 0.10 as in Tests Nos. 35 and 42. The upper limit of thepossible values of y is therefore 0.10.

The value of k in the formula of the major ingredient was set at 0.99 inTests Nos. 51 and 58. The resistivities of the resulting capacitors were3.0×10³ and 2.8×10³, both much lower than the desired lower limit of1.0×10⁷. Their Q factors were 1100 and 600, also falling far short ofthe criterion of at least 4500. The above criteria were all satisfiedwhen the value of k was increased to 1.00 as in Tests Nos. 52 and 59.The lowermost possible value of k is therefore 1.00. On the other hand,when the value of k was made as much as 1.05 as in Test No. 63, theresulting dielectric bodies were not coherently bonded on firing at ashigh a temperature as 1260° C. The desired electrical characteristicswere obtained when the value of k was reduced to 1.04 as in Tests Nos.57 and 62. Accordingly, the greatest possible value of k is 1.04.

We have ascertained from the results of Table 2 that the acceptablerange of the relative proportions of Li₂ O, SiO₂ and MO, the additivesof the ceramic compositions in accordance with our invention, can bedefinitely stated in reference to the ternary diagram of FIG. 2.

The point A in the ternary diagram indicates the Test No. 1 additivecomposition of zero mole percent Li₂ O, 65 mole percent SiO₂ and 35 molepercent MO. The point B indicates the Test No. 2 additive composition ofzero mole percent Li₂ O, 60 mole percent SiO₂ and 40 mole percent MO.The point C indicates the Test No. 3 additive composition of five molepercent Li₂ O, 45 mole percent SiO₂ and 50 mole percent MO. The point Dindicates the Test No. 4 additive composition of 50 mole percent Li₂ O,50 mole percent SiO₂ and zero mole percent MO. The point E indicates theTest No. 5 additive composition of 25 mole percent Li₂ O, 75 molepercent SiO₂ and zero mole percent MO.

The relative proportions of the additives Li₂ O, SiO₂ and MO of theceramic compositions in accordance with our invention are within theregion bounded by the lines sequentially connecting the above statedpoints A, B, C, D and E in the ternary diagram of FIG. 2.

Tables 1 and 2 prove that the additive compositions within the abovedefined region makes possible the provision of capacitors of the desiredelectrical characteristics. The additive compositions of Tests Nos. 6-10all fall outside that region, and the corresponding dielectric bodieswere not coherently bonded on firing at a temperature of 1290° C. Theabove specified acceptable range of the relative proportions of theadditives holds true regardless of whether only one of BaO. MgO, ZnO,SrO and CaO is employed as MO, as in Tests Nos. 11-15, or two or more orall of them are employed in suitable relative proportions as in otherTests.

Although we have disclosed our invention in terms of specific Examplesthereof, we understand that our invention is not to be limited by theexact details of such disclosure but admits of a variety ofmodifications or alterations within the usual knowledge of theceramists, chemists or electricians without departing from the scope ofthe invention. The following, then, is a brief list of such possiblemodifications or alterations:

1. The low temperature sinterable ceramic compositions of our inventionmay include various additives not disclosed herein. An example is amineralizer such as manganese dioxide. Used in a proportion (preferablyfrom 0.05 to 0.10 percent by weight) not adversely affecting the desiredcharacteristics of the resulting capacitors, such a mineralizer willlead to the improvement of sinterability.

2. The start material of the ceramic compositions in accordance with ourinvention may be substances such as oxides or hydroxides other thanthose employed in the foregoing Examples.

3. The temperature of the oxidizing heat treatment need not necessarilybe 600° C. but can be variously determined in a range (from 500° to1000° C. for the best results not exceeding the temperature of thepreceding sintering in a nonoxidative atmosphere, the oxidizingtemperature being dependent upon factors such as the particular basemetal electrode material in use and the degree of oxidation required forthe ceramic material.

4. The temperature of cosintering in a nonoxidative atmosphere may alsobe changed in consideration of the particular electrode material in use.We recommend a range of 1050° to 1200° C. if the electrode material isnickel, as we have ascertained from experiment that little or noflocculation of the nickel particles takes place in that temperaturerange.

5. The dielectric bodies an electrodes may be cosintered in a neutral,instead of reductive, atmosphere.

6. The ceramic compositions disclosed herein may be employed forcapacitors other than those of the multilayered configuration.

We claim:
 1. A low temperature sintered solid dielectric capacitorcomprising a dielectric ceramic body and at least two electrodes incontact therewith, the dielectric ceramic body consisting essentiallyof:(a) 100 parts by weight of a major ingredient expressed presesd bythe formula,

    {(Sr.sub.1-x Ca.sub.x)O}.sub.k (Ti.sub.1-y Zr.sub.y)O.sub.2,

wherex is a numeral in the range of 0.005 to 0.995 inclusive; k is anumeral in the range of 1.00 to 1.04 inclusive; and y is a numeral inthe range of 0.005 to 0.100 inclusive; and (b) From 0.2 to 10.0 parts byweight of an additive mixture of lithium oxide, silicon dioxide and atleast one metal oxide selected from the group consisting of bariumoxide, magnesium oxide, zinc oxide, strontium oxide and calcium oxide,the relative proportions of lithium oxide, silicon dioxide and at leastone selected metal oxide constituting the additive mixture being in thatregion of the ternary diagram of FIG. 2 attached hereto which is boundedby the lines sequentially connecting:the point A where the additivemixture consists of zero mole percent lithium oxide, 65 mole percentsilicon dioxide, and 35 mole percent metal oxide; the point B where theadditive mixture consists of zero mole percent lithium oxide, 60 molepercent silicon dioxide, and 40 mole percent metal oxide; the point Cwhere the additive mixture consists of five mole percent lithium oxide,50 mole percent silicon dioxide, and 45 mole percent metal oxide; thepoint D where the additive mixture consists of 50 mole percent lithiumoxide, 50 mole percent silicon dioxide, and zero mole percent metaloxide; and the point E where the additive mixture consists of 25 molepercent lithium oxide, 75 mole percent silicon dioxide, and zero molepercent metal oxide.
 2. A low temperature sintered solid dielectriccapacitor as set forth in claim 1, wherein the electrodes are buried inthe dielectric ceramic body.
 3. A low temperature sintered soliddielectric capacitor as set forth in claim 1, wherein the electrodes areof a base metal.
 4. A low temperature sintered solid dielectriccapacitor as set forth in claim 3, wherein the base metal is nickel. 5.A process for the manufacture of a low temperature sintered soliddielectric capacitor, which process comprises:(a) providing a mixtureof:100 parts by weight of a major ingredient, in finely divided form,that is expressed by the formula,

    {(Sr.sub.1-x Ca.sub.x)O}.sub.k (Ti.sub.1-y Zr.sub.y)O.sub.2,

wherex is a numeral in the range of 0.005 to 0.995 inclusive; k is anumeral in the range of 1.00 to 1.04 inclusive; and y is a numeral inthe range of 0.005 to 0.100 inclusive; from 0.2 to 10.0 parts by weightsof an additive mixture, in finely divided form, of lithium oxide,silicon dioxide and at least one metal oxide selected from the groupconsisting of barium oxide, magnesium oxide, zinc oxide, strontium oxideand calcium oxide, the relative proportions of boric oxide, silicondioxide and at least one selected metal oxide constituting the additivemixture being in that region of the ternary diagram of FIG. 2 attachedhereto which is bounded by the lines sequentially connecting:the point Awhere the additive mixture consists of zero mole percent lithium oxide,65 mole percent silicon dioxide, and 35 mole percent metal oxide; thepoint B where the additive mixture consists of zero mole percent lithiumoxide, 60 mole percent silicon dioxide, and 40 mole percent metal oxide;the point C where the additive mixture consists of five mole percentlithium oxide, 50 mole percent silicon dioxide, and 45 mole percentmetal oxide; the point D where the additive mixture consists of 50 molepercent lithium oxide, 50 mole percent silicon dioxide, and zero molepercent metal oxide; and the point E where the additive mixture consistsof 25 mole percent lithium oxide, 75 mole percent silicon dioxide, andzero mole percent metal oxide; (b) molding the mixture into desiredshape and size, the molding having at least two electrode portions of anelectroconductive material; (c) cosintering the molding and theelectrode portions to maturity in a nonoxidative atmosphere; and (d)reheating the cosintered molding and electrode portions in an oxidativeatmosphere.
 6. A process for the manufacture of a low temperaturesintered solid dielectric capacitor as set forth in claim 5, wherein theelectrode portions are formed on the molding by coating the same with anelectroconductive paste composed principally of a base metal.
 7. Aprocess for the manufacture of a low temperature sintered soliddielectric capacitor as set forth in claim 6, wherein the base metal isnickel.
 8. A process for the manufacture of a low temperature sinteredsolid dielectric capacitor as set forth in claim 5, wherein the moldingand the electrode portions are cosintered to maturity in a temperaturerange of 1000° to 1200° C.
 9. A process for the manufacture of a lowtemperature sintered solid dielectric capacitor as set forth in claim 5,wherein the cosintered molding and electrode portions are reheated in atemperature range of 500° to 1000° C.